In a human body the spinal column encloses the spinal cord and consists of a number of bones (called vertebrae) superimposed upon one another in a series which provides a flexible supporting column for the trunk and head. There are normally thirty-three vertebrae in humans, including the five that are fused to form the sacrum and the four coccygeal bones that form the tailbone. The upper three regions comprise the remaining twenty-four, and are grouped under the names cervical (seven vertebrae), thoracic (twelve vertebrae) and lumbar (five vertebrae), according to the regions they occupy.
Spinal fusion is a surgical technique in which one or more of the vertebrae of the spine are united together so that motion no longer occurs between them. Spinal fusion is done most commonly in the lumbar region of the spine, but it is also used to treat cervical and thoracic problems. Patients requiring spinal fusion have either neurological deficits or severe pain which has not responded to conservative treatment. Spinal fusion surgeries are also common in patients who suffer from moderate to severe back deformities that require reconstructive surgery.
The basic principle of spinal fusion surgery involves adding bone graft to an area of the spine to set up a biological response that causes the bone graft to grow between the two vertebral elements and create a fusion, thereby stopping the motion at that segment. The bone graft can be taken from the patient's hip or harvested from cadaver bone or manufactured as a synthetic bone graft.
In most cases, the fusion is augmented by a process called fixation, meaning the placement of metallic screws (pedicle screws often made from titanium), rods or plates, or cages to stabilize the vertebra to facilitate bone fusion. The fusion process typically takes six to twelve months after surgery. During this time external bracing may be required.
The pedicle screw provides a means of gripping a spinal segment. The screws themselves do not fixate the spinal segment, but act as firm anchor points that can then be connected with a rod. The screws are placed at two or three or multiple consecutive spine segments (e.g. lumbar segment 4 and 5) and then a rod is used to connect the screws. This prevents the motion at the segments that are being fused. After the bone graft grows, the pedicle screws and rods are no longer needed for stability and may be safely removed with a subsequent back surgery. However, most surgeons do not recommend removal unless the pedicle screws cause discomfort for the patient.
Pedicle screws are connected by plates or rods that span single or multiple vertebral segments. Crossbars may be added for additional strength. For multilevel fusion involving more than two vertebrae, rods are generally preferred over plates because rods can be individually cut and molded as required to facilitate maintenance of the alignment. The tips of pedicle screws should be embedded in the vertebral bone and should not breach the anterior vertebral body cortex.
It is important that the rods are of precise lengths for the patient and the spanned vertebrae. Various rod cutters are known in the prior art, for example Rinner U.S. Pat. No. 6,058,820 discloses a rod cutter having two force-applying members pivotally attached together. The cutters both have extending ends which are pivotally connected together and have rod cutting edges thereon.
Similarly GB 2463522 discloses a controlled feed mechanism attachable to a power tool, such as a surgical power tool, controls the rate at which a cutting tool such as a reamer is fed into a work piece, irrespective of the axial force applied by an operator or surgeon, by pulling itself along a threaded guide rod inserted in the workpiece. Various types of cutting tools may be fitted, including those used in hip resurfacing surgery such as a single pass cutter which permits the barrel cut, chamfer cut and end cut required to resurface the head of a femur to be made in one pass.
U.S. Pat. No. 5,988,027 discloses a manually operated surgical steel rod cutter. The rod cutter has a rod shearing tool head for cutting a rod when the rod is provided within aligned bores of two shearing subassemblies of the tool head. To cut the rod, an operator rotates an extendable handle to a substantially vertical position, inserts the rod in the tool head and rotates the handle to a substantially horizontal position.
Similarly US 20110107601 discloses a rod cutter apparatus which includes a rod holding plate having a rod opening for receiving a rod to be cut, a cutting member having a central opening defined by a cutting edge, the central opening being substantially aligned with the rod opening; and a drive assembly connected between the rod holding plate and the cutting member to cause oscillation of the cutting member relative to the rod holding plate, wherein oscillation of the cutting member relative to the rod holding plate cuts a rod in the rod opening.
The prior art teaches rod cutting systems which are table mounted and are manually operable. The prior art also includes systems which involve cutting the rods by using powered cutters. Most of the systems used in prior art uses scissor like blades which are moved either manually of by power to cut the rod outside the patient's body and then use it in the surgery. However, the prior art does not teach a rod cutter which is power operated and can be used in the surgery area in very tightly controlled manner.
In view of the limitations inherent in the available rod cutting systems, there exists a need for an improved surgical cutting system, capable of overcoming disadvantages inherent in conventional surgical cutting systems in a fast, robust, cost effective, secure, and environmental friendly manner. The present invention fulfils this need and provides further advantages as described in the following summary.